It is highly desired to obtain an isobutylene rich product, since that butene is useful in gasoline blending and subsequent reactions to produce, e.g., butyl rubber and lubricating oil additive. Crystalline aluminosilicates are known in the art to be useful for separating hydrocarbons. Particularly some of the Type X or Type Y zeolites have been disclosed which relate to the separation of olefins from paraffinic hydrocarbons and the separation of butene-1 from isobutylene (see U.S. Pat. Nos. 3,723,561 to Priegnitz and 4,119,678 to Neuzil et al). Zeolites, however, have the propensity to cause dimerization or even polymerization of olefins and are thus not well suited for use as an adsorbent for the separation of present interest.
We have made the discovery that silicalite is able to effect the separation of normal C.sub.4 hydrocarbons from isobutylene with substantially complete elimination of the aforementioned undesired side effects of dimerization and polymerization, particularly when pentene-1 is used to displace the normal C.sub.4 hydrocarbons from the silicalite.